Properties and morphology of bioceramics/poly(D,L‐lactide) composites modified by in situ compatibilizing extrusion

Composites of poly(D ,L ‐lactide) (PDLLA) with hydroxylapatite (HA) and PDLLA with tertiary calcium phosphate (TCP) were prepared by in situ modification with methylenediphenyl diisocyanate (MDI) and molded by piston extrusion at temperature between T_g and T_m of PDLLA. Mechanical properties of the composites increased obviously when compared with the unmodified bioactive ceramic particles/PDLLA composites. The effect of MDI contents on mechanical properties of the composites was studied. At the optimum conditions of 1.0/1.0molar ratios of ? NCO groups in MDI to ? OH groups in PDLLA, bending strength 68.4 MPa and bending modulus 2281.5 MPa, were achieved in composite HA/PDLLA/MDI with 15 wt % HA. Both increased by nearly 30% when compared with that of solution cast HA/PDLLA composites. Interfacial adhesion and compatibility between PDLLA and bioactive ceramic particles (HA and TCP) were investigated. Scanning electron microscopy (SEM) indicated that the interface between HA particles and PDLLA was blurred and HA particles were closely surrounded by PDLLA matrix in HA/PDLLA/MDI composites. Oriented fibrils along with longitudinal direction of extrusion die were also observed on the surfaces of HA/PDLLA/MDI composite. It is confirmed that MDI has improved interfacial adhesion and compatibility between HA particles and PDLLA phase. Fibril structures formed in the extrusion, and it contributed a great deal in enhancing the mechanical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4085–4091, 2006     

Enzymatic degradation of poly(D,L‐lactide) and its blends with poly(vinyl acetate)

The enzymatic degradation of poly(D ,L ‐lactide) (PLA) was investigated using two different lipases, Novozym 435 and Lipolase. The optimum temperature was 50°C for the enzymatic degradation of PLA. The effect of various solvents on the degradation of PLA was investigated at 50°C using Novozym 435, and toluene was found to be the best solvent among the solvents investigated. The enzymatic degradation of the blends of PLA and PVAc was investigated at 50°C in toluene. The enzymatic degradation of the blends of PLA and PVAc showed that there is an interaction between the polymers during degradation, which results in the reduction of degradation rate of both polymers in the blend. A continuous distribution model was used to determine the rate coefficients for polymer degradation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 657–680 2006     

Degradation of PLA,PLGA homo‐ and copolymers in the presence of serum albumin: a spectroscopic investigation

Poly(D,L ‐lactide‐co‐glycolide) samples with different glycolide contents, ie 85:15, 75:25 and 50:50 mole ratios of lactide to glycolide, and poly(L ‐lactide) were obtained from a commercial source. Polymer films of 15 µm thickness were prepared by a solvent‐casting method. Degradation studies were conducted at 37 °C in pH 7.4 phosphate buffered saline and in bovine serum albumin solution. The degradation behaviour of the films was followed by UV and FTIR spectrophotometry and viscometric and gravimetric measurements. Spectroscopic investigations showed that during the first month of degradation, both the chain length and the chain chemical structure changed, especially in the presence of bovine serum albumin. The short chains are attributed to the formation of new ester groups; however, the end‐groups may be aldehyde‐ or ketone‐like structures. While the intrinsic viscosities of all polymers decreased continuously after being exposed to the degradation media, insignificant mass loss occurred during the experimental investigation. © 2000 Society of Chemical Industry     

丙交酯合成工艺影响因素的分析

丙交酯是合成聚乳酸的主要原料,其收率和纯度制约着聚乳酸的成本和质量。介绍了聚乳酸的市场概况,重点综述了两步法丙交酯合成工艺的影响因素,分析了反应温度、压力、催化剂等对乳酸缩聚和解聚的影响以及粗丙交酯精制方法的优劣;分析了国内生产企业存在的问题和发展方向,提出丙交酯合成技术发展的关键在于开发高效手性催化剂、高收率的精制技术以及连续化生产工艺等。     

3-甲基吗啉-2,5-二酮与L-丙交酯共聚物的制备和表征

以辛酸亚锡为催化剂,合成了3-甲基吗啉-2,5-二酮(MMD)与L-丙交酯(L-LA)的共聚物,并用FT-IR、HNMR、粘度测定法对共聚物进行了表征.结果表明,氨基酸被引入到聚乳酸的主链中,且聚合物的组成可根据投料比例的不同在较大范围内调节.     

聚乳酸合成及改性研究进展

综述了近年来国内外聚乳酸直接合成法和丙交酯开环聚合法的研究进展,对聚乳酸改性方法进行了深入的总结和评述,并揭示了聚乳酸材料的研究开发前景。     

Nucleation Effects of Nucleobases on the Crystallization Kinetics of Poly(L‐lactide)

The effects of nucleobases, especially uracil, on the nonisothermal and isothermal crystallization, melting behavior, spherulite morphology, and crystalline structure of bio‐based and biodegradable PLLA are studied. The melt‐ and cold‐crystallization rates of PLLA increase with increasing uracil loading. The melting behavior of nonisothermally melt‐ and cold‐crystallized PLLAs depends on the uracil content. The isothermal crystallization kinetics is analyzed based on an Avrami model. The incorporation of uracil changes the t_1/2/T_c profile of PLLA due to the more distinct heterogeneous nucleation effects at small supercooling. The crystalline structure of PLLA is not affected by uracil presence. The nucleation density increases and the spherulite size decreases by uracil incorporation.

     

Poly(N‐isopropylacrylamide‐co‐hydroxyethyl methacrylate) graft copolymers and their application as carriers for drug delivery system

Poly(N‐isopropylacrylamide‐co‐hydroxyethyl methacrylate) [P(NIPAM‐co‐HEMA)] copolymer was synthesized by controlled radical polymerization from respective N‐isopropylacrylamide (NIPAM) and hydroxyethyl methacrylate (HEMA) monomers with a predetermined ratio. To prepare the thermosensitive and biodegradable nanoparticles, new thermosensitive graft copolymer, poly(L ‐lactide)‐graft‐poly(N‐isoporylacrylamide‐co‐hydroxyethyl methacrylate) [PLLA‐g‐P(NIPAM‐co‐HEMA)], with the lower critical solution temperature (LCST) near the normal body temperature, was synthesized by ring opening polymerization of L ‐lactide in the presence of P(NIPAM‐co‐HEMA). The amphiphilic property of the graft copolymers was formed by the grafting of the PLLA hydrophobic chains onto the PNIPAM based hydrophilic backbone. Therefore, the graft copolymers can self‐assemble into uniformly spherical micelles ò about 150–240 nm in diameter as observed by the field emission scanning electron microscope and dynamic light scattering. Dexamethasone can be loaded into these nanostructures during dialysis with a relative high loading capacity and its in vitro release depends on temperature. Above the LCST, most of the drugs were released from the drug‐loaded micelles, whereas a large amount of drugs still remains in the micelles after 48 h below the LCST. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of nucleation mechanism on complex poly(L‐lactide) nonisothermal crystallization process,part 2: Crystallization kinetics analysis

In the first part of this article, we reported the crystalline memory effect on the nonisothermal crystallization of poly(L ‐lactide). The experiments were carried out by using polymer single crystals growth from dilute solution as standard starting material. In this article (Part II), we have analyzed in detail the effect of the melting condition on the overall crystallization kinetics by applying the Nakamura‐Avrami model to DSC results. The absence or the low concentration of foreign infusible heterogeneous nuclei in our system allowed us to exalt the self‐nuclei role in polymer crystallization, to follow their concentration decrease during the melting process and to find the limiting melting temperature for their disappearance. Below such a temperature, a stable equilibrium number of self‐nuclei was observed, probably deriving from ordered structures, persisting in the melt, and originated from the single crystals thickening process during the polymer dynamic melting in the DSC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Construction of functional aliphatic polycarbonates for biomedical applications

Aliphatic polycarbonates are one important kind of biodegradable polymers and have been commonly used as integral components of engineered tissues, medical devices and drug delivery systems. As far as the biomedical application is concerned, traditional aliphatic polycarbonates usually suffer from the strong hydrophobicity, deficient functionality, and insufficient compatibility with cell/organs. Consequently, the application is quite limited in scope. Due to the imparted appealing properties, aliphatic polycarbonates bearing specifically designed functional/reactive groups attract great interest from researchers in the recent years. The present review outlines the development up to date concerning the design and biomedical application of functional aliphatic polycarbonates, with an emphasis on their ring-opening (co)polymerization preparation.